template function length will occur with debug

[augustheart]

I notice the template function
inline constexpr std::size_t length(CharT* s, std::size_t result = 0)
use tail call optimization. It can cause a stack overflow with debug because optimization was disabled.

[martinmoene]

Note to self: see also issue #22

[martinmoene]

Tested with:

#include "nonstd/string_view.hpp"
#include <iostream>

const int N = 10000;

std::string text( N, 'a' );

int main()
{
    std::cout
        << "nssv_CPLUSPLUS: " << nssv_CPLUSPLUS << '\n'
        << "length: " << nonstd::sv_lite::detail::length( text.c_str() );
}

// GNUC on Windows:
// g++ -std=c++11 -Wall -O0 -Wl,--stack,100 -I../../../include -Dnssv_CONFIG_SELECT_STRING_VIEW=nssv_STRING_VIEW_NONSTD -o issue.exe issue.cpp && issue.exe

// MSVC 14.0 (VS2015) and higher: 
// cl -EHsc -W4 -Od -F100 -Gs256 -D"_DEBUG" -MDd -I../../../include -Dnssv_CONFIG_SELECT_STRING_VIEW=nssv_STRING_VIEW_NONSTD issue.cpp && issue.exe